Integrated SequencePhysics Chemistry Organic Biology

Web Resources

  click if a link is broken

Special points of emphasis

Work, Energy, and Power


As we discussed earlier within Newton's Laws, there are two main types of gravity problems, those in which the gravitational force is virtually constant over the distances involved and those in which the gravitational force changes with varying position within the system.

Each of these different models has a different approach to energy. The manner of describing changes in energy is different in a constant force system versus a system where force changes with position.

In both cases, however, as work is done against or by the field, as the object is changing position, its state of potential energy is changing. As two attracting objects are moved further apart, the potential energy of the system increases whether an object is being raised from the surface of the Earth or whether two objects are separating in outer space.

On the surface of the Earth, where the distances over which the object is going to move will be relatively small, it is more convenient to assign zero as the potential energy on the ground.

For situations in outer space, however, where the force can be seen to decrease the further apart the objects are moved, zero potential energy represents the state of the objects when they are infinitely far apart. All other values are negative. Think about this. Make sure you understand this.

In both cases, potential energy increases with increasing separation, and if you applied the outer space model to the object near the Earth's surface, you would compute the same change in energy. The outer space model is the more descriptive of reality, because it shows gravitational potential energy as a form of binding energy. Two objects under the influence of mutual gravitation have fallen into a potential energy well together. They have fallen together into the well of their mutual binding energy. The magnitude of negative potential energy shows how much energy would have to be imparted to the system to allow the objects to escape from each other.

Work, Energy, and Power


As we discuss the fundamental principles of Work, Power & Energy, keep in mind that electrostatic systems will be a primary field of application for these concepts. When a positive charge is moved towards another positive charge, potential energy increases. Energy is being stored in the system. However, when a negative charge is moved towards a positive charge, potential energy decreases and the system is losing potential energy.

The behavior of oppositely charged particles, distinguished by a force of mutual attraction, is similar to gravitational force. The energy description of oppositely charged particles is analogous to the behavior of two masses interacting through gravitational force. The nearer the objects, the lower the potential energy with both gravitational force between masses and the electric force between unlike charges.

The WikiPremed MCAT Course is a free comprehensive course in the undergraduate level general sciences. Undergraduate level physics, chemistry, organic chemistry and biology are presented by this course as a unified whole within a spiraling curriculum.

Please read our policies on privacy and shipping & returns.  Contact Us.
MCAT is a registered trademark of the Association of American Medical Colleges, which does not endorse the WikiPremed Course.

Creative Commons License
The work of WikiPremed is published under a Creative Commons Attribution Share Alike 3.0 License. There are elements of work here, such as a subset of the images in the archive from WikiPedia, that originated as GNU General Public License works, so take care to follow the unique stipulations of that license in printed reproductions. You can use the resources here for commercial or non-commercial purposes, but please give attribution and a link to the production credits and edit history of the resource. For the works here which began as my individual work, please attribute "John Wetzel, an author at".